Golf ball resin compositions are employed particularly as cover-forming materials that are injection-molded over the ball core. In such applications, it is important to ensure that the resin composition has a fluidity suitable for injection molding. One key property of the resin composition is thus the melt flow rate (MFR). Suitable adjustment of the MFR is particularly important in cases where the cover is to be formed to a thickness (gauge) of less than 1.0 mm. When the desired MFR can be obtained, the golf ball ultimately produced often is able to achieve both a reduced spin rate and a good durability (scuff resistance).
Various modifiers and additives are typically compounded in resin compositions for golf balls. For example, a number of disclosures relate to the use of compounds having a fluorene skeleton as additives. In one such disclosure, JP-A 2002-509161, a fluorene derivative is included as a visible-light initiator within a golf ball material. In addition, JP-A 2013-94666 and JP-A 2013-94668 teach art that includes, within a core-forming material, an organic fluorescent material selected from a group of compounds having fluorene skeletons.
However, the compounds with fluorene skeletons mentioned in these prior-art publications are intended for use as visible-light initiators or organic fluorescent materials. They are not intended for use in adjusting the melt flow rate of resin compositions.
Also, JP No. 4514491 discloses art which, in order to reclaim plastic materials containing spent (used) polymer, ensures practical properties such as flame retardancy and mechanical characteristics by including, as a compatibilizing agent, a compound having a fluorene skeleton.
However, the foregoing art neither teaches nor even mentions the ability to both ensure a good fluidity and also achieve ball properties such as a reduced ball spin rate and good scuff resistance by including a compound having a fluorene skeleton within a golf ball resin material, particularly a resin composition for golf ball covers having a small gauge.